The traditional monolithic RF base transceiver station (BTS) architecture is increasingly being replaced by a distributed BTS architecture in which the functions of the BTS are separated into two physically separate units—a baseband unit (BBU) and a remote radio head (RRH). The BBU performs baseband processing for the particular air interface that is being used to wirelessly communicate over the RF channel. The RRH performs radio frequency processing to convert baseband data output from the BBU to radio frequency signals for radiating from one or more antennas coupled to the RRH and to produce baseband data for the BBU from radio frequency signals that are received at the RRH via one or more antennas.
The RRH is typically installed near the BTS antennas, often at the top of a tower, and the BBU is typically installed in a more accessible location, often at the bottom of the tower. The BBU and the RRH are typically connected through one or more fiber optic links. The interface between the BBU and the RRH is defined by front-haul communication link standards such as the Common Public Radio Interface (CPRI) family of specifications, the Open Base Station Architecture Initiative (OBSAI) family of specifications, and the Open Radio Interface (ORI) family of specifications.
Wireless operators are under constant pressure to increase the speed, capacity and quality of their networks while continuing to hold the line on cost. As technologies evolve, the challenge is becoming increasingly difficult. For example, the frequency spectrum available to these operators is a scarce resource. As the use of the available frequency spectrum increases, any network or non-network induced interference may limit the ability of service providers to provide services that meet consumer demands for speed, capacity and quality. Interference can be caused by unintended (i.e. rogue, spurious) transmission in the licensed band or inter-modulation signals generated from the intended RF transmissions.
When an intermodulation signal in the downlink or other interference signal overlap in frequency-time with the uplink desired signal, it could be difficult to isolate or detect the presence of the interfering signal by just looking at a plot of the uplink spectrum. Spectral estimation becomes more complex when desired signals are bursty in nature in the frequency-time domain plane. Long-Term Evolution (LTE) 4G air interface is such a protocol where the uplink and downlink frequency-time assignment changes very frequently—almost every millisecond. In the case of passive inter-modulation, the downlink intermodulation signal can end up in the uplink band for certain band arrangements. For most wireless protocols, it is hard to identify the downlink intermodulation from the uplink signal if it is overlapped in time and frequency.
Therefore, there is a need in the art for techniques to monitor and manage interference so that wireless networks can provide services over their limited spectrum to meet consumer demands for speed, capacity and quality.